Project Abstract T cell-based immunotherapies to treat cancer have shown outstanding promise in the clinic for many patients, but there are still barriers hindering these therapies from reaching full potential. Strategies to enhance T cell infiltration, persistence and effector function within the tumor are necessary, as the immunosuppressive, hostile nature of the tumor microenvironment (TME) serves to dampen immune responses. Extracellular adenosine triphosphate (eATP) is a major component of the TME and has varying effects on the tumor and immune cells infiltrating the tumor. P2RX7 is a puringeric receptor involved in eATP-sensing and is best known for its role in ?danger signal? recognition, triggering immune cell activation and, in some scenarios, cell death. Our lab has reported that P2RX7 eATP-sensing is essential for memory CD8+ T cell differentiation, maintenance and function due to its important role in promoting mitochondrial health. This led us to investigate whether the beneficial effects of P2RX7 on CD8+ T cell metabolic fitness would be applicable to CD8+ T cell responses in tumor immunotherapy. Our preliminary data demonstrated that P2RX7 deficient CD8+ T cells fail to effectively control melanoma tumors, correlating with fewer P2rx7-/- CD8+ T cells within the tumor site and aberrant increased expression of markers associated with T cell exhaustion. These data indicated that P2RX7 was important for CD8+ T cell tumor immune responses. However, it is also known that P2RX7 overstimulation with very high eATP concentrations, such as those in the TME, results in lymphocyte death, suggesting that P2RX7 may eventually become a liability to survival of donor T cells and overall tumor control. Therefore, we hypothesize that initial P2RX7 signaling is important for priming an effective CD8+ T cell response allowing for T cell maintenance and function within the tumor. Furthermore, we hypothesize that we can boost CD8+ T cell activity by altering P2RX7 signaling pharmacologically at different times during the anti-tumor immune response. These hypotheses will be tested in the following specific aims: (1) Determine role of P2RX7 activation in CD8+ T cell infiltration, persistence and function within tumors, and (2) Effects of pharmacological P2RX7 agonism/antagonism on anti-tumor activity of CD8+ T cells. The results of this proposal will help elucidate the complicated role of P2RX7 in CD8+ T cell tumor immunity and will inform whether P2RX7 could be targeted as a novel therapeutic approach in adoptive cell therapy regimens.